Re: [PATCH v4] ksmbd: fix possible memory leak in smb2_lock()

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On 15/2/2023 09:04, Namjae Jeon wrote:
2023-02-14 15:36 GMT+09:00, Hangyu Hua <hbh25y@xxxxxxxxx>:
argv needs to be free when setup_async_work fails or when the current
process is woken up.

Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Signed-off-by: Hangyu Hua <hbh25y@xxxxxxxxx>
---

v2: avoid NULL pointer dereference in set_close_state_blocked_works()
v3: avoid race condition between smb2_lock() and smb2_cancel()
v4: use another way to avoid race condition

  fs/ksmbd/smb2pdu.c   | 20 +++++++++++++-------
  fs/ksmbd/vfs_cache.c |  2 ++
  2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
index d681f91947d9..1b517d3ca2ef 100644
--- a/fs/ksmbd/smb2pdu.c
+++ b/fs/ksmbd/smb2pdu.c
@@ -6666,7 +6666,8 @@ int smb2_cancel(struct ksmbd_work *work)
  				    "smb2 with AsyncId %llu cancelled command = 0x%x\n",
  				    le64_to_cpu(hdr->Id.AsyncId),
  				    le16_to_cpu(chdr->Command));
-			cancel_work = iter;
+			if (iter->cancel_fn)
+				cancel_work = iter;
You have freed ->cancel_argv in smb2_lock().  Wouldn't this cause UAF
issue the below?

         if (cancel_work) {
                 cancel_work->state = KSMBD_WORK_CANCELLED;
                 if (cancel_work->cancel_fn)
                         cancel_work->cancel_fn(cancel_work->cancel_argv);
         }
I think this can't cause UAF beacause cancel_fn will be set to NULL before releasing argv in smb2_lock(). There is no way to use a argv.

  			break;
  		}
  		spin_unlock(&conn->request_lock);
@@ -7050,6 +7051,7 @@ int smb2_lock(struct ksmbd_work *work)
  						      smb2_remove_blocked_lock,
  						      argv);
  				if (rc) {
+					kfree(argv);
  					err = -ENOMEM;
  					goto out;
  				}
@@ -7061,6 +7063,16 @@ int smb2_lock(struct ksmbd_work *work)

  				ksmbd_vfs_posix_lock_wait(flock);

+				spin_lock(&work->conn->request_lock);
+				spin_lock(&fp->f_lock);
+				if (work->state != KSMBD_WORK_CLOSED) {
I think that this check is not needed if we don't delete entry in
set_close_state_blocked_works().
+					list_del(&work->fp_entry);
+					work->cancel_fn = NULL;
+					kfree(argv);
+				}
+				spin_unlock(&fp->f_lock);
+				spin_unlock(&work->conn->request_lock);
+
  				if (work->state != KSMBD_WORK_ACTIVE) {
  					list_del(&smb_lock->llist);
  					spin_lock(&work->conn->llist_lock);
@@ -7069,9 +7081,6 @@ int smb2_lock(struct ksmbd_work *work)
  					locks_free_lock(flock);

  					if (work->state == KSMBD_WORK_CANCELLED) {
-						spin_lock(&fp->f_lock);
-						list_del(&work->fp_entry);
-						spin_unlock(&fp->f_lock);
  						rsp->hdr.Status =
  							STATUS_CANCELLED;
  						kfree(smb_lock);
@@ -7093,9 +7102,6 @@ int smb2_lock(struct ksmbd_work *work)
  				list_del(&smb_lock->clist);
  				spin_unlock(&work->conn->llist_lock);

-				spin_lock(&fp->f_lock);
-				list_del(&work->fp_entry);
-				spin_unlock(&fp->f_lock);
  				goto retry;
  			} else if (!rc) {
  				spin_lock(&work->conn->llist_lock);
diff --git a/fs/ksmbd/vfs_cache.c b/fs/ksmbd/vfs_cache.c
index da9163b00350..761a8aa540ce 100644
--- a/fs/ksmbd/vfs_cache.c
+++ b/fs/ksmbd/vfs_cache.c
@@ -372,6 +372,8 @@ static void set_close_state_blocked_works(struct
ksmbd_file *fp)
  		list_del(&cancel_work->fp_entry);
  		cancel_work->state = KSMBD_WORK_CLOSED;
  		cancel_work->cancel_fn(cancel_work->cancel_argv);
+		cancel_work->cancel_fn = NULL;
+		kfree(cancel_work->cancel_argv);
If we remove list_del, we don't need to do them here ? and we can
change _safe version to list_for_each().

Agreed. I will move this list_del() to smb2_lock() in v5.

Thanks,
Hangyu

  	}
  	spin_unlock(&fp->f_lock);
  }
--
2.34.1





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